1. Field of the Invention
This invention relates to an ink jet type recording apparatus and method in which ink droplets are jetted to form images on a recording medium such as a recording sheet, and more particularly to an ink jet head and ink supplying apparatus used in an ink jet type recording apparatus and an ink jet recording and ink supplying method in which phase-change ink called "hot-melt ink" is used.
2. Prior Art
With the increasing numbers of computers, fax machines, and copiers in today's society, there is a growing demand for high quality reproduction and print quality on different recording medium. Such demand necessitates the efficient supply of ink to recording apparatus and the development of better means for transferring the ink to a recording medium.
Ink jet heads using a "hot-melt" ink have been disclosed in prior patent applications. U.S. Pat. No. 4,593,292, U.S. Pat. No. 4,631,557 and U.S. Pat. No. 4,609,924 disclose such ink jet heads. These ink jet heads require a plate-shaped heater located in an intermediate ink pool whose purpose is to heat the entire head which is constructed out of materials with high coefficients of thermal conductivity. This heater is typically located outside the walls forming the ink supplying path, resulting in a large thermal loss, and requiring a large capacity heater. Further, reducing the preparation time between the application of voltage and the start of the printing operation is difficult. This interval is the ink preheating period. Another difficulty encountered in these kinds of ink jet heads is that, when the solid-phase ink is changed to a liquid-phase ink, bubbles tend to form in the ink. If the bubbles remain in the ink supplying path, they reduce pressure and the jetting of the ink may not be satisfactory.
Methods of supplying ink to hot-melt ink jet heads which make use of the phase change involving the heating of a solid-phase ink are disclosed in U.S. Pat. No. 4,593,292 and U.S. Pat. No. 4,636,803.
The method of application No. 98546/1986 discloses heating a part of a solid-phase block of ink in order to form liquid-phase ink which is transferred into an ink pooling chamber. The amount of ink supplied is likely to be affected by the ambient temperature. Because the time interval between the start of the ink heating device and the end of the ink supplying operation is lengthy, the ink supplying device, which is located on the carriage, must be operated during printing and kept connected to the ink pooling chamber. Another flaw in this method is that part of the ink liquefied in the ink supplying device but not supplied to the ink pooling chamber resolidifies in the ink supplying device, possibly blocking or partially blocking the operation of the ink pushing cylinder. Another possible obstruction is the portion of the solid-phase ink which is softened and deformed by heating and is located between the liquid and solid portions.
The method of U.S. Pat. No. 4,636,803 discloses allowing solid-phase ink particles or pellets to drop into the ink pooling chamber. However, at high temperatures, it is possible for these particles or pellets to soften and join together, obstructing the ink supplying operation. To overcome this difficulty, solid-phase ink pellets are loaded in the ink supplying device so that they are separated from one another. However, loading the pellets in the ink supplying device is difficult, particularly because volumetric capacity of the ink container is small.
The ink used for an ink jet recording apparatus is a solid at room temperature and, when heated, melts into tacky, liquid-phase ink capable of being jetted in the form of ink droplets. U.S. Pat. Nos. 4,636,803; 4,682,185; and 4,631,557 are examples of related art. U.S. Pat. No. 4,636,803 discloses a device and method in which block-shaped ink, not loaded on the carriage, is supplied at a predetermined rate to the ink jet head. U.S. Pat. No. 4,682,185 discloses a device and method in which bar-shaped solid-phase ink, loaded on the carriage, is fed in to the ink jet head which melts the ink. U.S. Pat. No. 4,631,557 discloses a device and method in which a cartridge containing solid-phase ink is mounted on the ink jet head and the ink is melted by a heater located in the head.
In the conventional ink jet head and ink jet recording method in which the solid-phase ink is liquefied outside the head, it is necessary to provide both a heater for liquefying the ink and one to heat the head and maintain it at high temperature. This arrangement is disadvantageous because it requires an excessive amount of space, consumes more power than is desirable, and costs more to manufacture as an additional circuit is needed for the heater.
Conventional systems where the solid-phase is liquified in the ink jet head, also have disadvantages. First, the ink melting position is set away from the nozzle section for jetting the ink. Also the contact area of the ink melting member is small compared to the volume of the solid-phase ink. Therefore, the space occupied by the components to be heated is large, the amount of heat necessary to heat them is correspondingly large, and the heating time is long. Secondly, the liquid-phase ink deteriorates because it is held in large quantity in the head at high temperature for a prolonged period of time. The last drawback to this method is that the liquid ink may leak out of the ink jet head should the head fall down accidentally.
In other prior art, the ink is supplied to the head through flexible tube-shaped members. The ink in the tube-shaped member is often affected by acceleration and deceleration of the carriage on which the ink jet head is mounted, thus varying the ink pressure in or near a pressure generator. Also, the ink is isolated from the outside air when it is supplied to the pressure generator. The ink is thus affected by the bubbles formed in the ink supplying path, and the ink jet head is therefore not too reliable. In addition, clogging is possible because of the long distance between a filter and the ink jet.